With current treatment options, the five-year survival rate for patients with AML is only 25%, thus understanding mechanisms of relapse and resistance is important therapeutically. The most common aberration in AML results in activation of the fms-like receptor 3 (Flt3-ITD), which was recently shown to alter the redox environment of cancer cells. While these changes remain poorly understood, elevations of reactive oxygen species can promote the cancer phenotype. Heme oxygenase 1 (HO-1) is a ROS-induced anti-oxidant that can also inhibit apoptosis and promote metabolism leading to cell survival and drug resistance. Our preliminary data suggest that, Flt3-ITD-expressing cells contain elevated constitutive expression of HO-1 as compared to Flt3-wildtype (WT) expressing cells. Further, knockdown of HO-1 with siRNA results in decreased proliferation and viability of Flt3-ITD expressing cells. We hypothesize that Flt3-ITD-dependent kinase signaling and ROS production increase constitutive expression of HO-1, leading to activation of anti- oxidant and anti-apoptotic pathways and resulting in proliferation and drug resistance in AML. To test our hypothesis, we will 1) Determine the molecular mechanisms by which HO-1 is constitutively expressed in Flt3- ITD positive AML and the functional consequences of this expression and 2) Elucidate the role of HO-1 in therapeutic resistance of AML. The isogenic BaF3 Flt3-WT and Flt3-ITD cell lines will be used in combination with human Flt3-ITD positive AML cell lines MOLM-13 and MV4.11 to test both specific aims. To complete Aim 1, we will examine the Flt3-kinase and ROS dependence of HO-1 expression in Flt3-ITD positive cells. Transcriptional regulation of HO-1 expression will also be evaluated. In vitro findings will be further assessed ex vivo utilizing tisue microarray specimens from AML patients. The effects of HO-1 expression on Flt3-ITD positive AML will be delineated utilizing chemical and genetic inhibitors of HO-1. For Aim 2, we will determine the contribution of HO-1 to chemoresistance of Flt3-ITD expressing cells utilizing the afore mentioned HO-1 inhibition methods. Using similar techniques, we will also evaluate the contribution of HO-1 to de novo and acquired resistance to the Flt3 inhibitors lestaurtinib and sorafenib. These studies together will provide a greater understanding of the redox mechanisms underlying Flt3-ITD expressing AML, and will better equip us to therapeutically target the biological pathways that promote AML progression and drug resistance. PUBLIC HEALTH RELEVANCE: The proposed studies address a research area that has largely been unstudied and focuses on the role of an antioxidant, HO-1, in growth, survival, and drug resistance of Flt3-ITD positive acute myeloid leukemia (AML). This research is relevant to public health because understanding how antioxidants can contribute to growth, survival and drug resistance of cancer cells will enhance our ability to clinically treat the 30% of AML patient whose disease expresses the Flt3-ITD mutation, and possibly extend the life expectancy of patients diagnosed with this disease.